Winter tyre

ABSTRACT

A winter tyre is described having a tread band wherein a plurality of blocks configured to obtain optimal performance both on snow-covered roads and on dry and wet roads in specific conditions of use (in particular during acceleration, braking or cornering with high power vehicles). Each of the aforementioned blocks has at least one sipe that defines two adjacent block portions in the respective block, each block portion having a respective surface facing the sipe. The surface has a radially outer portion having a profile which is substantially undulating, a radially inner portion also having a profile which is substantially undulating and an intermediate portion arranged between the radially outer portion and the radially inner portion and having a profile which is substantially rectilinear.

The present invention relates to a winter tyre.

Such a tyre is preferably intended to be mounted on wheels of high powerand speed vehicles, like for example SUVs or particularly heavy sportscars.

A winter tyre typically comprises a tread band on which a plurality ofcircumferential and transversal grooves are formed. Such grooves delimita corresponding plurality of blocks. Each of such blocks generally has aplurality of sipes. Each sipe defines in the respective block twoadjacent block portions separated by the sipe.

The function of the sipes is essentially to offer further gripping edgeson the snow-covered ground and to hold a certain amount of snow insidethem, so as to offer a friction with the snow on the road surfacegreater than that offered by the tread band itself. Moreover, thanksalso to the greater softness of the mixture typically used in wintertyres with respect to that typically used in summer tyres, and to themobility of the two block portions defined by each sipe, the sipes allowthe winter tyre to adapt better to the snow-covered road surface.Overall, thanks to the sipes it is possible to achieve an improvement inthe performance of the tyre during acceleration, braking, cornering andas far as the lateral grip on a snow-covered road surface is concerned.

The provision of the sipes does, however, reduce the performance of thetyre on a snow-free road surface, be it dry or wet.

This reduction in performance is considered to be due to the fact thatthe different portions of the block separated by the sipes, being ableto move with respect to one another, are not capable of offeringsufficient resistance to tangential (or “shear”) stresses applied to theblock during acceleration, cornering or braking on a snow-free roadsurface, with consequent deformation of the block and reduction of itscontact surface with the road surface itself.

The expression “circumferential” or “circumferentially” is usedreferring to a direction substantially parallel to the rolling directionof the tyre, i.e. a direction substantially parallel to the axial middleplane of the tyre.

The expression “axial” or “axially” is used referring to a directionsubstantially parallel to the rotation axis of the tyre, i.e. adirection substantially perpendicular to the axial middle plane of thetyre.

The expression “radial” or “radially” is used referring to a directionsubstantially perpendicular to the rotation axis of the tyre andbelonging to a plane containing such a rotation axis.

The expression “longitudinal” or “longitudinally” is used referring to amain direction of extension of the sipe.

The expression “lateral stress”, with reference to the tyre, or to theblocks, or to the sipes, is used to indicate a stress acting, on a planetangent to the tyre, along a direction that is tilted with respect tothe longitudinal direction.

The expression “profile which is substantially rectilinear” is used,referring to any surface portion of the sipe or of the blocks, toindicate that such a surface portion lies substantially on a plane or isshifted from such a plane by a negligible distance with respect to thelongitudinal and radial dimensions of the same surface portion. Such adistance is considered negligible when it is not greater than onetwentieth of the overall longitudinal extension of the surface portion.

The expression “profile which is substantially undulating” is used, withreference to any surface portion, to indicate the line defined, on anincident plane parallel both to the longitudinal direction of the sipeand to a plane tangent to the aforementioned surface portion, by asequence of curvilinear or rectilinear lengths, which, going from a linedefined by the intersection of the aforementioned incident plane with areference plane different from said incident plane, progressively moveapart from such a line until a first maximum shift point is reached, tothen progressively move towards the aforementioned line until a nullshift point is reached, such a sequence of lengths then proceeding withthe same profile on the opposite side with respect to the aforementionedline and so on.

The “profile which is substantially undulating” can thus be defined byan alternating sequence of lengths that, in the aforementioned incidentplane, create a line comprising an alternating sequence of portions withopposite concavity, wherein each of such portions can be defined both bya curved line and by a zigzag broken line.

As a particular case of a surface having a “profile which issubstantially undulating” a surface comprising an alternating sequenceof concave and convex portions is herein referred to.

Each concave and convex portion has, in the aforementioned incidentplane, a maximum shift point from the aforementioned reference plane.The plurality of maximum shift points defined in each concave and convexportion when sectioning such a concave and convex portion with aplurality of incident planes that are parallel to one another defines acrest of the respective concave or convex portion.

The expression “transversal section” is used to refer to a sectiondefined by any plane inclined by any angle with respect to thelongitudinal direction of the sipe. Preferably, such an inclined planeis perpendicular to the longitudinal direction of the sipe.

JP 2003-118322 describes a winter tyre comprising a tread band in whichat least one sipe comprises a corrugated or zigzag portion extendingalong a direction and a flat portion at the opposite sides of thecorrugated portion along said direction. In an alternative embodiment,the flat portion is arranged under the corrugated portion.

WO 2012/164449 describes a winter tyre comprising a tread band on whicha plurality of grooves is provided, at least one block delimited by theplurality of grooves, at least one sipe formed on the block andextending between a top and a bottom of the sipe and shaped so as todefine, on each block portion separated by the sipe, a first surfacefacing the other block portion and extending from the top to anintermediate depth of the sipe, which has an undulating profile, and asecond surface facing the other block portion, radiused to the firstsurface and extending from the intermediate depth up to the bottom,which has a rectilinear profile.

WO 2012/164450 describes a winter tyre provided with sipes shaped so asto define, on each block portion separated by a sipe, a first surfacefacing the other block portion and extending from the top to anintermediate depth of the sipe and a second surface facing the otherblock portion, radiused to the first surface and extending from theintermediate depth up to the bottom, in which the first surface has aprofile which is rectilinear and the second surface has a profile whichis undulating.

Hereafter reference will be made without distinction to the sipes or toone (or both) of the surfaces of the block portions separated by eachsipe and facing the sipe itself. Indeed, the profile of theaforementioned surfaces matches the profile of the sipe.

The Applicant has realised that, in order to obtain optimal performanceof the tyre during acceleration, braking or cornering on a snow-coveredroad surface, it is advantageous to provide the tyre with sipes whoseradially outer portion has a profile which is substantially undulating.The Applicant has indeed observed that the profile which issubstantially undulating has a greater linear extension, under the samelongitudinal extension, with respect to a profile which is substantiallyrectilinear and, therefore, offers a greater gripping edge on thesnow-covered road surface and greater ability to hold snow.

The Applicant has also noted that the provision in the sipes of aprofile which is substantially undulating, ensuring a mutualinterconnection between the two block portions separated by each sipe,determines a high rigidity of the blocks with respect to lateralstresses and, consequently, excellent behavior of the tyre as far as thelateral stability on a snow-covered road surface is concerned.

The Applicant has, however, noted that the provision in the tyre ofsipes having a profile which is substantially undulating involves adegradation in the performance of the tyre as far as the lateralstability on a snow-free road surface is concerned when such a tyre issubjected to lateral stresses of a certain degree. The Applicant hasattributed such a degradation to the excessive abrasion occurring on thetwo block portions separated by each sipe due to the mutual sliding ofsuch block portions when they are subjected to the aforementionedlateral stresses.

The Applicant has noted that, in order to improve the aforementionedperformance on a snow-free road surface, without penalizing theaforementioned performance on a snow-covered road surface, it isadvantageous to use sipes having a substantially rectilinear profilearranged in a radially inner position with respect to a substantiallyundulating profile. The Applicant has indeed observed that the provisionof a substantially rectilinear profile makes it possible to minimize theabove-discussed sliding, thus reducing the negative effects producedthereby.

However, the Applicant has verified that, particularly in extremelateral stress conditions on a snow-free road surface, like for examplein the case of rapid and sudden turning with particularly powerful andheavy vehicles, problems of lateral stability remain in those tyresprovided with sipes of the type described for example in WO 2012/164449.

The Applicant attributes the cause of such problems to an excessiveyielding and mobility of the blocks at the respective radially innerportions thereof.

The Applicant has realised that in order to greatly improve theperformance of the tyre as far as the lateral stability on a snow-freeroad surface is concerned it is necessary to have a good interconnectionbetween the radially inner portions of the two block portions separatedby each sipe.

The Applicant has perceived that it is possible to obtain suchinterconnection by providing, in the radially inner portions of theblocks, a profile which is substantially undulating.

The Applicant has, however, verified that it is appropriate to keep in afirst radially outer portion of the sipe a profile which issubstantially undulating and in a second more radially inner portionwith respect to the aforementioned first portion a profile which issubstantially rectilinear. This is in order to achieve all of thepositive effects (described above) produced by such profiles on asnow-covered road surface and on a snow-free road.

The Applicant has finally found that it is possible to greatly improvethe performance of the tyre as far as the lateral stability on asnow-free road surface is concerned and under extreme stress conditions,at the same time ensuring optimal behavior on a snow-covered roadsurface during acceleration, braking or cornering and regarding thelateral grip, providing the tyre with sipes having both at a radiallyouter portion thereof and at a radially inner portion thereof a profilewhich is substantially undulating, such sipes also having at a radiallyintermediate portion thereof arranged between said radially outerportion and said radially inner portion a profile which is substantiallyrectilinear.

The present invention therefore relates to, in an aspect thereof, awinter tyre comprising a tread band wherein a plurality of blocks isdefined, at least some of said blocks comprising at least one sipeextending from a top portion of the block towards a bottom portion ofthe block.

Preferably, said at least one sipe defines two adjacent block portionsin the block, each of said two block portions comprising a surfacefacing said at least one sipe.

Preferably, said surface comprises a radially outer portion having afirst profile which is substantially undulating.

Preferably, said surface comprises a radially inner portion having asecond profile which is substantially undulating.

Preferably, said surface comprises an intermediate portion arrangedbetween said radially outer portion and said radially inner portion andhaving a third profile which is substantially rectilinear.

The Applicant believes that the provision of a profile which issubstantially undulating both at the radially outer portion and at theradially inner portion of the sipes ensures high interconnection betweenthe block portions separated by the sipes, with consequent high rigidityof the block and, therefore, better response of the tyre to allstresses, even extreme ones, which the tyre is subjected to when usedboth on a snow-covered road surface and on a snow-free road surface. Atthe same time, the interposition of a substantially rectilinear profilebetween the aforementioned substantially undulating profiles ensuresadequate control of mutual sliding of the block portions separated byeach sipe when the block is subjected to extreme lateral stresses,nullifying the negative effects produced by such sliding.

The present invention, in the aforementioned aspect, can have at leastone of the preferred characteristics indicated hereafter, bothindividually and in combination.

Preferably, said first profile and second profile are defined by aplurality of concave and convex portions arranged in an alternatingsequence along a direction parallel to a longitudinal direction of saidat least one sipe. In this way the desired interconnection between theblock portions separated by the sipes is ensured along the entirelongitudinal extension of each sipe.

Preferably, said longitudinal direction is parallel to a plane which istangent to a radially outer surface of said tread band at said two blockportions facing said sipe. The radial extension of each sipe istherefore constant in the entire tread band, thus guaranteeinghomogeneous behavior of the tyre on a snow-covered road surface.

More preferably, said longitudinal direction is tilted with respect toboth an axial direction and a circumferential direction of the tyre. Inthis way, the rigidity given to the blocks by the interconnection of thetwo block portions defined by each sipe produces its advantageouseffects both in response to axial stresses, like for example in the caseof a sudden turn, and in response to circumferential stresses, like forexample in the case of sudden acceleration or braking.

Preferably, said intermediate portion defines a reference plane.

Preferably, said reference plane substantially coincides with a radialplane of the tyre.

In preferred embodiments of the present invention, said concave andconvex portions extend on opposite sides with respect to said referenceplane.

Preferably, said concave and convex portions extend symmetrically onopposite sides with respect to said reference plane.

Preferably, each of the concave and convex portions of the first profilehas a respective first crest whose distance from said reference planeprogressively increases moving away in a radial direction from saidintermediate portion to said top portion.

Preferably, each of the concave and convex portions of the secondprofile has a respective second crest whose distance from said referenceplane progressively increases moving away in a radial direction fromsaid intermediate portion towards said bottom portion.

Preferably, the distance of said first crest from said reference planeis substantially null at said intermediate portion.

Preferably, the distance of said second crest from said reference planeis substantially null at said intermediate portion.

In a preferred embodiment of the present invention, said surface has, ina transversal section taken at each concave portion of the firstprofile, a respective convex portion of the second profile and, in atransversal section taken at each convex portion of the first profile, arespective concave portion of the second profile.

In this case, the overall profile of the sipe is such that, in eachtransversal section of the sipe, the first profile and the secondprofile are arranged on opposite sides with respect to theaforementioned reference plane.

Preferably, said tread band comprises a central annular portion astrideof an axial middle plane and two annular shoulder portions arranged onaxially opposite sides with respect to the central annular portion, thecentral annular portion being separated from each annular shoulderportion by a respective circumferential groove.

Preferably, the sipe described above is provided on the blocks of saidcentral annular portion and of only one of said annular shoulderportions.

More preferably, when the tyre is mounted on a rim forming a wheel of amotor vehicle, said annular shoulder portion is axially more externalthan the central annular portion with respect to said motor vehicle.

The Applicant has in fact verified that the sipe described above withreference to the first preferred embodiment of the present invention,produces its advantageous effects when provided in the portions of thetyre identified above. The blocks of the other annular shoulder portionof the tyre can in this case be provided with sipes of a different type,for example of a type similar to the sipes described in WO 2012/164450.

In further embodiments of the present invention, said surface has, in atransversal section taken at each concave portion of the first profile,a respective concave portion of the second profile and, in a transversalsection taken at each convex portion of the first profile, a respectiveconvex portion of the second profile.

In this case, the overall profile of the sipe is such that, in eachtransversal section of the sipe, the first profile and the secondprofile are arranged on the same side with respect to the aforementionedreference plane.

The Applicant has verified that the sipe described above with referenceto the further preferred embodiments of the present invention producesits advantageous effects when provided on one of the annular shoulderportions of tyres of the “directional-type”, i.e. in tyres that, in use,are stressed mainly at one of the two annular shoulder portions.

In another preferred embodiment of the present invention, each of theconcave and convex portions of the second profile comprises a radiallyouter surface portion, a radially inner surface portion and anintermediate surface portion arranged between said radially outersurface portion and said radially inner surface portion, wherein saidintermediate surface portion is substantially parallel to said referenceplane.

The Applicant has verified that providing such a profile at the radiallyinner portion of the sipe ensures a greater interconnection effectbetween the adjacent block portions, with consequent further stiffeningof the blocks.

Preferably, each of the concave and convex portions of the secondprofile has a respective third crest whose distance from said referenceplane progressively increases moving away in a radial direction from theaforementioned intermediate portion to said intermediate surfaceportion.

More preferably, the distance of said third crest from said referenceplane progressively decreases moving away in a radial direction fromsaid intermediate surface portion towards said bottom portion.

Preferably, the distance of said third crest from said reference planeis substantially null at said intermediate portion.

In a further preferred embodiment of the present invention, said surfacehas, in a transversal section taken at each concave portion of the firstprofile, a respective concave portion of the second profile and, in atransversal section taken at each convex portion of the first profile, arespective convex portion of the second profile.

The Applicant has verified that such a sipe carries out its advantageouseffects when foreseen in the blocks of the annular shoulder portions ofthe tyre. The blocks of the central annular portion of the tyre can inthis case be provided with sipes of a different type, for example of atype similar to the sipes described in WO 2012/164449.

In another preferred embodiment of the present invention, said surfacehas, in a transversal section taken at each concave portion of the firstprofile, a respective convex portion of the second profile and, in atransversal section taken at each convex portion of the first profile, arespective concave portion of the second profile.

Preferably, said tread band comprises a central annular portion astrideof an axial middle plane and two annular shoulder portions arranged onaxially opposite sides with respect to the central annular portion, thecentral annular portion being separated from each annular shoulderportion by a respective circumferential groove, wherein said at leastone sipe is provided only on the blocks of said annular shoulderportions.

The Applicant has verified that such a sipe particularly produces itsadvantageous effects when provided in the blocks of the annular shoulderportions of the tyre. The blocks of the central annular portion of thetyre can in this case be provided with sipes of a different type, forexample of the type similar to the sipes described in WO 2012/16449and/or WO 2012/16450.

In a different embodiment, said tread band comprises a central annularportion astride of an axial middle plane and two annular shoulderportions arranged on axially opposite sides with respect to the centralannular portion, the central annular portion being separated from eachannular shoulder portion by a respective circumferential groove, whereinsaid at least one sipe is provided only on the blocks of said centralannular portion.

Preferably, when said surface is sectioned with an incident plane, saidfirst profile and second profile define respective lines which aresubstantially sinusoidal.

In further preferred embodiments of the present invention, when saidsurface is sectioned with an incident plane, said first profile andsecond profile define respective zigzag broken lines.

Preferably, said zigzag broken lines comprise an alternating sequence ofa first rectilinear length and a second rectilinear length.

Further characteristics and advantages of the present invention willbecome clearer from the following detailed description of its preferredembodiments, made with reference to the attached drawings. In suchdrawings:

FIG. 1 is a schematic perspective view of a significant portion of atyre in accordance with an exemplifying embodiment of the presentinvention;

FIG. 2 is a schematic perspective view, in an enlarged scale, of a partof a block of the tyre of FIG. 1;

FIGS. 3 a, 3 b and 3 c are schematic views, respectively from above(FIG. 3 a), in a transversal section taken along the reference planeA1-A1 of FIG. 3 a (FIG. 3 b) and in perspective (FIG. 3 c), of a firstembodiment of a sipe used in the tyre of FIG. 1;

FIGS. 4 a, 4 b and 4 c are schematic views, respectively from above(FIG. 4 a), in a transversal section taken along the reference planeA1-A1 of FIG. 4 a (FIG. 4 b) and in perspective (FIG. 4 c), of a secondembodiment of a sipe used in the tyre of FIG. 1;

FIGS. 5 a, 5 b and 5 c are schematic views, respectively from above(FIG. 5 a), in a transversal section taken along the reference planeA1-A1 of FIG. 5 a (FIG. 5 b) and in perspective (FIG. 5 c), of a thirdembodiment of a sipe used in the tyre of FIG. 1;

FIGS. 6 a, 6 b and 6 c are schematic views, respectively from above(FIG. 6 a), in a transversal section taken along the reference planeA1-A1 of FIG. 6 a (FIG. 6 b) and in perspective (FIG. 6 c), of a fourthembodiment of a sipe used in the tyre of FIG. 1.

With reference to FIG. 1, reference numeral 1 wholly indicates anexemplifying embodiment of a tyre in accordance with the presentinvention.

The tyre 1 comprises a carcass structure (not visible) arrangedtoroidally around an axis Z (substantially coinciding with the rotationaxis of the tyre), a belt structure (not visible) arranged in a radiallyouter position with respect to the carcass structure and a tread band 2arranged in a radially outer position with respect to the belt structureand having a radially outer surface 3 configured to come into contactwith a road surface on which the tyre 1 is intended to roll.

On the tread band 2 a central annular portion C astride of an axialmiddle plane (not shown) and two annular shoulder portions S1, S2arranged on axially opposite sides with respect to the central annularportion C can be identified. The central annular portion C is separatedfrom each annular shoulder portion S1, S2 by a respectivecircumferential groove 4. The portion S1 is the one that, when the tyre1 is mounted on a wheel of a motor vehicle, is located in an axiallyouter position with respect to the central annular portion C from thevehicle.

Further grooves, also generically indicated with 4, extending alongcircumferential and transversal directions are also provided on thetread band 2. All of the grooves 4 delimit a plurality of blocks 5 whichare arranged in sequence preferably along a circumferential direction Y.

On each block 5 one or more sipes 6 are provided, the sipes extendingalong a longitudinal direction X that, like in the embodiment hereindescribed and illustrated, can be tilted with respect both to the axialdirection Z and to the circumferential direction Y.

For example, the longitudinal direction X can be tilted with respect tothe axial direction Z by an angle a that is preferably greater thanabout 2°, more preferably greater than about 5° (FIGS. 3 a, 4 a, 5 a and6 a). The angle α is preferably lower than about 45°, more preferablylower than about 40°. Even more preferably, the angle α is comprisedbetween about 2° and about 45°, more preferably between about 5° andabout 40°, for example equal to about 35°.

The aforementioned longitudinal direction X is preferably parallel to aplane which is tangent to the radially outer surface 3 of the tread band2 at two block portions 9, 10, facing said sipe 6.

For the sake of simplicity of illustration, reference numerals 4, 5 and6 are associated with just some of the grooves, blocks and sipes,respectively.

Alternative embodiments of the tyre 1 in which the blocks 5 havedifferent configuration and orientation from those illustrated hereinand in which the sipes 6 have different longitudinal extension andorientation from those illustrated herein are provided.

Preferably, each sipe 6 is open, at the opposite longitudinal ends 6 a,6 b, on a pair of grooves 4 that delimit the block 5 itself, so that thesipe 6 crosses through the block 5 from one side to the other.

As shown in FIG. 2, each sipe 6 extends between a top portion 7 of theblock 5, open on the radially outer surface 3 of the tread band 2, and abottom portion 8 of the block 5, defined in a radially inner position ofthe tread band 2.

Each sipe 6 defines, in the block 5, said two block portions, which arerespectively indicated with 9 and 10.

Such a block portions are adjacent to one another, separated by the sipe6 and spaced apart by an amount m that is kept substantially constantalong the longitudinal direction X of the sipe 6 (FIGS. 3 a, 4 a, 5 aand 6 a).

Such a measurement m is for example greater than about 0.1 mm, morepreferably greater than about 0.2 mm. The measurement m is preferablylower than about 0.8 mm, more preferably lower than about 0.6 mm. Evenmore preferably, the measurement m is comprised between about 0.1 mm andabout 0.8 mm, more preferably between about 0.2 mm and about 0.6 mm, forexample equal to about 0.4 mm.

Each block portion 9, 10 comprises a respective surface facing the sipe6. Such a surface is configured identically to the sipe 6, so that whatis said herein below with reference to the sipe 6 applies in anabsolutely identical manner to each of the aforementioned surfaces andvice-versa.

At least some of the sipes 6 of the tyre 1 are shaped as describedbelow.

FIGS. 3 a, 3 b and 3 c show a first embodiment of the sipe 6.

Such a sipe 6 comprises a radially outer portion 61, a radially innerportion 62 and an intermediate portion 63 arranged between the radiallyouter portion 61 and the radially inner portion 62.

The radially outer portion 61 and the radially inner portion 62 bothhave a profile which is substantially undulating, whereas theintermediate portion 63 has a profile which is substantiallyrectilinear.

Hereafter, the profile of the radially outer portion 61 is indicated as“first profile” and the profile of the radially inner portion 62 isindicated as “second profile”.

The intermediate portion 63 is substantially flat. It defines in theblock 5 a reference plane, indicated in FIGS. 3 a and 3 b with P. Such areference plane P is parallel to the longitudinal direction X of thesipe 6 and preferably coincides with a radial plane of the tyre 1.

The radial extension h3 of the intermediate portion 63 is equal to afraction of the overall radial extension H of the sipe 6. Preferably,the overall radial extension H is greater than 4 times the radialextension h3 of the intermediate portion 63. Preferably the overallradial extension H is greater than 5 times the radial extension h3 ofthe intermediate portion 63. For example, H can be equal to about 7 mmand h3 can be equal to about 1 mm.

Preferably, the intermediate portion 63 is arranged at a distance h1from the top portion 7 of the block 5 comprised between about 1 mm andabout 4 mm and at a distance h2 from the bottom portion 8 of the block 5comprised between about 1 mm and about 10 mm, more preferably betweenabout 2 mm and about 6 mm. For example, h1 and h2 can be equal to about3 mm.

The first profile is suitably radiused to the intermediate portion 63and is defined by a plurality of concave 61 a and convex 61 b portionsarranged in alternating sequence along a direction parallel to thelongitudinal direction X of the sipe 6. Preferably, the concave 61 a andconvex 61 b portions extend symmetrically on opposite sides with respectto the reference plane P.

Similarly, the second profile is suitably radiused to the intermediateportion 63 and is defined by a plurality of concave 62 a and convex 62 bportions arranged in alternating sequence along the aforementioneddirection parallel to the longitudinal direction X of the sipe 6, suchconcave 62 a and convex 62 b portions preferably extending symmetricallyon opposite sides with respect to the reference plane P.

For the sake of simplicity of illustration, reference numerals 61 a, 61b are associated with just some of the aforementioned concave portionsand references numerals 62 a, 62 b are associated with just some of theaforementioned convex portions.

The sipe 6 shown in FIGS. 3 a, 3 b and 3 c is shaped so that, in anytransversal section of the sipe 6 (like for example the transversalsection from which FIG. 3 b originates) the first profile and the secondprofile are arranged on opposite sides with respect to the referenceplane P. With specific reference to FIG. 3 b, the shape of the sipe 6 isthus such that, on the section plane, at each concave portion 61 a ofthe first profile there is a respective convex portion 62 b of thesecond profile and at each convex portion 61 b of the first profilethere is a respective concave portion 62 a of the second profile.

Moving along the longitudinal direction X of the sipe 6, at a centralportion of each of the concave 61 a and convex 61 b portions of thefirst profile there is a respective crest 610 a, 610 b whose distancefrom the reference plane P progressively increases (preferably linearly)moving away from the intermediate portion 63 in the radial directionuntil the top portion 7 of the block 5 is reached. Similarly, at acentral portion of each of the concave 62 a and convex 62 b portions ofthe second profile there is a respective crest 620 a, 620 b whosedistance from the reference plane P progressively increases (preferablylinearly) moving away from the intermediate portion 63 in the radialdirection towards the bottom portion 8 of the block 5.

The crests 610 a and 610 b thus consist, in each of the concave 61 a, 62a and convex 61 b, 62 b portions of the first profile and of the secondprofile, respectively, of plurality of points belonging to incidentplanes that are parallel to one another (each point belonging to one ofsaid planes, so that the aforementioned points are aligned) having themaximum distance from the reference plane P with respect to the distancefrom the aforementioned reference plane of any other point of therespective concave 61 a, 62 a and convex 61 b, 62 b portion belonging tothe same incident plane.

Preferably, at the intermediate portion 63 the distance A of the crests610 a, 610 b, 620 a, 620 b from the reference plane P is substantiallynull, whereas at the top 7 and bottom 8 portions of the block 5 thedistance A of the crests 610 a, 610 b, 620 a, 620 b from the referenceplane P is comprised between about 0.5 mm and about 2 mm, preferablybetween about 1 mm and about 1.5 mm, for example equal to about 1.25 mm.

The first profile and the second profile extend along the longitudinaldirection X of the sipe 6 for a length comprised between 50% and 100% ofthe entire longitudinal extension of the sipe 6. In the case in whichthere are areas of the sipe 6 not having the aforementioned profiles,such areas are coplanar to the intermediate portion 63 and arepreferably provided both upstream and downstream of the aforementionedprofiles along the longitudinal direction X (i.e. at the oppositelongitudinal ends 6 a, 6 b of the sipe 6). In this case, preferably, theareas upstream and downstream have identical longitudinal and radialextensions.

In the embodiments herein illustrated, the first profile is configuredso that, when sectioned with any incident plane, a zigzag broken line isobtained, which is clearly shown in FIG. 3 a.

Preferably, the zigzag broken line comprises an alternating sequence offirst and second rectilinear lengths, respectively indicated with 101and 102, radiused together so that the broken line has, at the crests610 a, 610 b, 620 a, 620 b, rounded vertices.

Preferably, the first and second rectilinear lengths 101, 102 extendsubstantially parallel to the axial direction Z and to thecircumferential direction Y, respectively. In particular, there is amaximum shifting from the axial direction Z of about 2° and a maximumshifting from the circumferential direction Y of about 5°.

Moreover, all of the first rectilinear lengths 101 preferably have asubstantially constant extension D, for example comprised between about1.5 mm and about 10 mm, preferably between about 2 mm and about 6 mm,for example equal to about 4 mm, whereas the second rectilinear lengths102 preferably have an extension d shorter than that of the firstrectilinear lengths, for example comprised between 1.5 mm and about 10mm, preferably between about 2 mm and about 5 mm, for example equal toabout 3.5 mm.

The sipe 6 of FIGS. 3 a, 3 b and 3 c has a preferred use in the blocks 5of the central annular portion C and of the annular shoulder portion S1,in an axially outer position with respect to the vehicle on which thewheel comprising the tyre 1 is mounted. The blocks 5 of the annularshoulder portion S2 can in this case be provided with sipes of adifferent type, for example of the type similar to the sipes describedin WO 2012/164450.

FIGS. 4 a, 4 b and 4 c schematically show an alternative embodiment ofthe sipe 6 used in the tyre 1 of the present invention.

In such a figure, structural and functional elements that are identicalto those described above with reference to FIGS. 3 a, 3 b and 3 c aremarked with the same reference numeral and are not described anyfurther.

The sipe 6 of FIGS. 4 a, 4 b and 4 c differs from that of FIGS. 3 a, 3 band 3 c only in that, in any transversal section of the sipe 6 (like forexample the transversal section from which FIG. 4 b originates) thefirst profile and the second profile are arranged on the same side withrespect to the reference plane P. With particular reference to FIG. 4 b,the shape of the sipe 6 is thus such that, on the section plane, at eachconcave portion 61 a of the first profile there is a respective concaveportion 62 b of the second profile and at each convex portion 61 b ofthe first profile there is a respective convex portion 62 a of thesecond profile.

The sipe 6 of FIGS. 4 a, 4 b and 4 c has a preferred use in the blocks 5of one of the shoulder portions S1, S2 of a tyre 1 of the“directional-type”.

FIGS. 5 a, 5 b and 5 c and FIGS. 6 a, 6 b, 6 c schematically show twofurther alternative embodiments of the sipe 6 used in the tyre 1 of thepresent invention.

In such figures, structural and functional elements that are identicalto those described above with reference to FIGS. 3 a, 3 b and 3 c aremarked with the same reference numeral and are not described anyfurther.

The sipe 6 of FIGS. 5 a, 5 b and 5 c and of FIGS. 6 a, 6 b, 6 c differsfrom that of FIGS. 3 a, 3 b and 3 c only for the different shape of thesecond profile and for the different radial dimensions of the radiallyouter portion 61, of the radially inner portion 62 and of theintermediate portion 63.

In particular, each of the concave portions 62 a of the second profilecomprises a radially outer surface portion 72 a, a radially innersurface portion 73 a and an intermediate surface portion 74 a.Similarly, each of the convex portions 62 b of the second profilecomprises a radially outer surface portion 72 b, a radially innersurface portion 73 b and an intermediate surface portion 74 b arrangedbetween the radially outer surface portion 72 b and the radially innersurface portion 73 b.

In any transversal section of the sipe 6, the intermediate surfaceportions 74 a, 74 b are substantially rectilinear and are apart from thereference plane P by the distance A discussed above.

The radially outer surface portions 72 a, 72 b and the radially innersurface portions 73 a, 73 b are properly radiused to the intermediatesurface portions 74 a, 74 b.

The crest 610 a, 610 b of each of the concave 62 a and convex 62 bportions of the second profile has a distance from the reference plane Pthat progressively increases (preferably linearly) moving away in theradial direction from the intermediate portion 63 up to the intermediatesurface portion 74 a, 74 b, to then proceed parallel to the referenceplane P at the intermediate surface portion 74 a, 74 b and finallyprogressively decrease (preferably linearly) moving away from theintermediate surface portion 74 a, 74 b in the radial direction towardsthe bottom portion 8 of the block 5. Preferably, such a distance issubstantially null at the intermediate portion 63 and at the bottomportion 8.

The radial extension h3 of the intermediate portion 63 is preferablylower than (for example half) the radial extension h3 of the sipe 6shown in FIGS. 3 a, 3 b, 3 c, the radial extension H being equal. Forexample, in the embodiments shown in FIGS. 5 a, 5 b, 5 c and 6 a, 6 b, 6c h3 it can be equal to about 0.5 mm.

Preferably, the intermediate portion 63 is arranged at a distance h1from the top portion 7 of the block 5 that is lower than the distance h1of the sipe 6 shown in FIGS. 3 a, 3 b, 3 c, the overall radial extensionH being equal. Consequently, the intermediate portion 63 is arranged ata distance h3 from the bottom portion 8 of the block 5 that is greaterthan the distance h2 of the sipe 6 shown in FIGS. 3 a, 3 b, 3 c, theoverall radial extension H being equal. For example, in the embodimentsshown in FIGS. 5 a, 5 b, 5 c and 6 a, 6 b, 6 c h1 can be equal to about2 mm and h2 can be equal to about 4.5 mm.

Preferably, the intermediate surface portion 74 a, 74 b has a radialextension h2′″ which is equal to the radial extension h3 of theintermediate portion 63. For example, h2′″ can be equal to about 0.5 mm.

Preferably, the intermediate surface portion 74 a,74 b is arranged at adistance h2″ from the intermediate portion 63 that is equal to thedistance h2″ from the bottom portion 8. For example h2′ and h2″ can beequal to about 2 mm.

With particular reference to FIGS. 5 a, 5 b, 5 c, the sipe 6 shown insuch figures has a configuration such that, like in the embodiment ofFIGS. 4 a, 4 b and 4 c, in any transversal section of the sipe 6 (likefor example the transversal section from which FIG. 5 b originates) thefirst profile and the second profile are arranged on the same side withrespect to the reference plane P. On the section plane, therefore, ateach concave portion 61 a of the first profile there is a respectiveconcave portion 62 b of the second profile and at each convex portion 61b of the first profile there is a respective convex portion 62 a of thesecond profile.

The sipe 6 of FIGS. 5 a, 5 b and 5 c has a preferred use in the blocks 5of the annular shoulder portions S1, S2 of the tyre 1. The blocks of thecentral annular portion C can in this case be provided with sipes of adifferent type, for example of the type similar to the sipes describedin WO 2012/164449.

On the other hand, with particular reference to FIGS. 6 a, 6 b, 6 c, thesipe 6 shown in such figures has a configuration such that, like in theembodiment of figures 3 a, 3 b and 3 c, in any transversal section ofthe sipe 6 (like for example the transversal section from which FIG. 6 boriginates) the first profile and the second profile are arranged onopposite sides with respect to the reference plane P. On the sectionplane, therefore, at each concave portion 61 a of the first profilethere is a respective convex portion 62 b of the second profile and ateach convex portion 61 b of the first profile there is a respectiveconcave portion 62 a of the second profile.

The sipe 6 of FIGS. 6 a, 6 b and 6 c has a preferred use in the blocks 5of the annular shoulder portions S1 and S2 of the tyre 1. The blocks ofthe central annular portion C can in this case be provided with sipes ofa different type, for example of a type similar to the sipes describedin WO 2012/16449 and/or WO 2012/16450.

The sipe 6 of FIGS. 6 a, 6 b and 6 c can also have an use in the blocks5 of the central annular portion C of the tyre 1. The blocks of theannular shoulder portions S1 and S2 can in this case be provided withsipes of a different type, for example of a type similar to the sipesdescribed in WO 2012/16449 and/or WO 2012/16450.

Of course, a man skilled in the art can make further modifications andvariants to the invention described above in order to satisfy specificand contingent use requirements, said variants and modifications in anycase being within the scope of protection as defined by the followingclaims.

1. A winter tyre, comprising a tread band wherein a plurality of blocksis defined, at least some of said blocks comprising at least one sipeextending from a top portion of the block towards a bottom portion ofthe block, wherein said at least one sipe defines two adjacent blockportions in the block, each of said two block portions comprising asurface facing said at least one sipe, said surface comprising: aradially outer portion having a first profile which is substantiallyundulating; a radially inner portion having a second profile which issubstantially undulating; an intermediate portion arranged between saidradially outer portion and said radially inner portion and having athird profile which is substantially rectilinear.
 2. The tyre accordingto claim 1, wherein said first profile and second profile are defined bya plurality of concave and convex portions arranged in an alternatingsequence along a direction parallel to a longitudinal direction said atleast one sipe.
 3. The tyre according to claim 2, wherein saidlongitudinal direction is parallel to a plane which is tangent to aradially outer surface of said tread band at said two block portionsfacing said sipe.
 4. The tyre according to claim 2, wherein saidlongitudinal direction is tilted with respect to both an axial directionand a circumferential direction of the tyre.
 5. The tyre according toclaim 1, wherein said intermediate portion defines a reference planesubstantially coinciding with a radial plane of the tyre.
 6. The tyreaccording to claim 2, wherein said intermediate portion defines areference plane substantially coinciding with a radial plane of the tyreand wherein said concave and convex portions extend symmetrically onopposite sides with respect to said reference plane.
 7. The tyreaccording to claim 5, wherein each of the concave and convex portions ofthe first profile has a respective first crest whose distance from saidreference plane progressively increases moving away in a radialdirection from said intermediate portion to said top portion.
 8. Thetyre according to claim 7, wherein the distance of said first crest fromsaid reference plane is substantially null at said intermediate portion.9. The tyre according to claim 2, wherein said intermediate portiondefines a reference plane substantially coinciding with a radial planeof the tyre and wherein each of the concave and convex portions of thesecond profile has a respective second crest whose distance from saidreference plane progressively increases moving away in a radialdirection from said intermediate portion towards said bottom portion.10. The tyre according to claim 9, wherein the distance of said secondcrest from said reference plane is substantially null at saidintermediate portion.
 11. The tyre according to claim 2, wherein saidsurface has, in a transversal section taken at each concave portion ofthe first profile, a respective convex portion of the second profileand, in a transversal section taken at each convex portion of the firstprofile, a respective concave portion of the second profile.
 12. Thetyre according to claim 1, wherein said tread band comprises a centralannular portion astride of an axial middle plane and two annularshoulder portions arranged on axially opposite sides with respect to thecentral annular portion, the central annular portion being separatedfrom each annular shoulder portion by a respective circumferentialgroove, wherein said at least one sipe is provided on the blocks of saidcentral annular portion and of only one of said annular shoulderportions.
 13. The tyre according to claim 12, wherein when the tyre ismounted on a rim forming a wheel of a motor vehicle, said annularshoulder portion is axially more external than the central annularportion with respect to said motor vehicle.
 14. The tyre according toclaim 2, wherein said surface has, in a transversal section taken ateach concave portion of the first profile, a respective concave portionof the second profile and, in a transversal section taken at each convexportion of the first profile, a respective convex portion of the secondprofile.
 15. The tyre according to claim 2, wherein said intermediateportion defines a reference plane substantially coinciding with a radialplane of the tyre and wherein each of the concave and convex portions ofthe second profile comprises a radially outer surface portion, aradially inner surface portion and an intermediate surface portionarranged between said radially outer surface portion and said radiallyinner surface portion, wherein said intermediate surface portion issubstantially parallel to said reference plane.
 16. The tyre accordingto claim 15, wherein each of the concave and convex portions of thesecond profile has a respective third crest whose distance from saidreference plane progressively increases moving away in a radialdirection from said intermediate portion to said intermediate surfaceportion.
 17. The tyre according to claim 16, wherein the distance ofsaid third crest from said reference plane progressively decreasesmoving away in a radial direction from said intermediate surface portiontowards said bottom portion.
 18. The tyre according to claim 16, whereinthe distance of said third crest from said reference plane issubstantially null at said intermediate portion.
 19. The tyre accordingto claim 15, wherein said surface has, in a transversal section taken ateach concave portion of the first profile, a respective concave portionof the second profile and, in a transversal section taken at each convexportion of the first profile, a respective convex portion of the secondprofile.
 20. The tyre according to claim 15, wherein said surface has,in a transversal section taken at each concave portion of the firstprofile, a respective convex portion of the second profile and, in atransversal section taken at each convex portion of the first profile, arespective concave portion of the second profile.
 21. The tyre accordingto claim 14, wherein said tread band comprises a central annular portionastride of an axial middle plane and two annular shoulder portionsarranged on axially opposite sides with respect to the central annularportion, the central annular portion being separated from each annularshoulder portion by a respective circumferential groove, wherein said atleast one sipe is provided only on the blocks of said annular shoulderportions.
 22. The tyre according to claim 14, wherein said tread bandcomprises a central annular portion astride of an axial middle plane andtwo annular shoulder portions arranged on axially opposite sides withrespect to the central annular portion, the central annular portionbeing separated from each annular shoulder portion by a respectivecircumferential groove, wherein said at least one sipe is provided onlyon the blocks of said central annular portion.
 23. The tyre according toclaim 1, wherein when said surface is sectioned with an incident plane,said first profile and second profile define respective lines which aresubstantially sinusoidal.
 24. The tyre according to claim 1, whereinwhen said surface is sectioned with an incident plane, said firstprofile and second profile define respective zigzag broken lines. 25.The tyre according to claim 24, wherein said zigzag broken linescomprise an alternating sequence of a first rectilinear length and asecond rectilinear length.
 26. The tyre according to claim 6, whereineach of the concave and convex portions of the second profile has arespective second crest whose distance from said reference planeprogressively increases moving away in a radial direction from saidintermediate portion towards said bottom portion.
 27. The tyre accordingto claim 6, wherein each of the concave and convex portions of thesecond profile comprises a radially outer surface portion, a radiallyinner surface portion and an intermediate surface portion arrangedbetween said radially outer surface portion and said radially innersurface portion, wherein said intermediate surface portion issubstantially parallel to said reference plane.
 28. The tyre accordingto claim 14, wherein each of the concave and convex portions of thesecond profile comprises a radially outer surface portion, a radiallyinner surface portion and an intermediate surface portion arrangedbetween said radially outer surface portion and said radially innersurface portion, wherein said intermediate surface portion issubstantially parallel to said reference plane.